Microelectronic assembly with pre-disposed fill material and associated method of manufacture

ABSTRACT

A microelectronic substrate assembly and method for manufacture. In one embodiment, bond members (such as solder balls) project away from a surface of the microelectronic substrate to define a fill region or cavity between the surface of the microelectronic substrate and the bond members. A fill material is disposed in the fill region, for example, by dipping the microelectronic substrate in reservoir of fill material so that a portion of the fill material remains attached to the microelectronic substrate. An exposed surface of the fill material is engaged with a support member, such as a printed circuit board, and the bond members are attached to corresponding bond pads on the support member. The microelectronic substrate and the fill material can then be encapsulated with an encapsulating material to form a device package.

This application is a divisional of pending U.S. patent application Ser.No. 09/651,448, filed on Aug. 30, 2000 now U.S. Pat. No. 6,576,495.

TECHNICAL FIELD

The present invention relates to microelectronic substrate packageshaving a pre-disposed fill material for mounting the package to asupporting member.

BACKGROUND

Packaged microelectronic assemblies, such as memory chips andmicroprocessor chips, typically include a microelectronic substrate dieencased in a plastic, ceramic or metal protective covering. The dieincludes functional devices or features, such as memory cells, processorcircuits and interconnecting wiring. The die also typically includesbond pads electrically coupled to the functional devices. The bond padscan be coupled to pins or other types of terminals that extend outsidethe protective covering for connecting to buses, circuits, and/or othermicroelectronic assemblies.

One conventional “flip chip” package 10 shown in plan view in FIG. 1includes a microelectronic die 20 having a downwardly facing surface 24with solder ball pads 22, and an upwardly facing surface 23 opposite thedownwardly facing surface 24. Solder balls 21 are attached to the solderball pads 22 and dipped in flux. The die 20 is then positioned with thedownwardly facing surface 24 facing toward a printed circuit board (PCB)30 to engage the solder balls 21 with corresponding bond pads 31 on thePCB 30. The solder balls 21 are partially melted or “reflowed” andsolidified to form structural and electrical bonds with the bond pads 31on the PCB 30.

In one aspect of the arrangement shown in FIG. 1, a gap correspondingroughly to the diameter of the solder balls 21 remains between the uppersurface of the PCB 30 and the downwardly facing surface 24 of the die 20after the die 20 has been attached. The gap can be detrimental to theintegrity and performance of the die 20 because it can allow oxidizingagents and other contaminants to attack the solder ball bond between thedie 20 and the PCB 30. Furthermore, the gap can reduce the rate at whichheat is transferred away from the die 20, reducing the life expectancyand/or the performance level of the die 20.

To alleviate the foregoing drawbacks, an underfill material 40 istypically introduced into the gap between the die 20 and the PCB 30. Forexample, in one conventional approach, a bead of flowable epoxyunderfill material 40 is positioned on the PCB 30 along two edges of thedie 20. The underfill material 40 is heated until it flows and fills thegap by capillary action, as indicated by arrows “A.” The underfillmaterial 40 can accordingly protect the solder ball connections fromoxides and other contaminants, and can increase the rate at which heatis transferred away from the die 20. The underfill material 40 can alsoincrease the rigidity of the connection between the die 20 and the PCB30 to keep the package 10 intact during environmental temperaturechanges, despite the fact that the die 20, the solder balls 21 and thePCB 30 generally have different coefficients of thermal expansion.

One drawback with the capillary action approach described above forapplying the underfill material 40 is that the underfill material 40 cantake up to 20 minutes or longer to wick its way to into the gap betweenthe die 20 and the PCB 30. Accordingly, the capillary underfill processcan significantly increase the length of time required to produce thepackages 10. One approach to addressing this drawback (typicallyreferred to as a “no-flow” process) is to first place the underfillmaterial directly on the PCB 30 and then place the die 20 on theunderfill material. For example, as shown in FIG. 2A, a quantity ofunderfill material 40 a having an integrated quantity of flux can bedisposed on the PCB 30 adjacent to the bond pads 31. As shown in FIG.2B, the die 20 can be lowered onto the PCB 30 until the solder balls 21contact the bond pads 31 of the PCB 30. As the solder balls 21 approachthe bond pads 31, the die 20 contacts the underfill material 40 a andsqueezes the underfill material 40 a outwardly around the solder balls21 and between the downwardly facing surface 24 of the die 20 and theupper surface of the PCB 30, as indicated by arrows “B”. Anencapsulating material 70 is then disposed on the die 20 and the PCB 30.

One problem with the no-flow process described above with reference toFIGS. 2A-2B is that air bubbles can become trapped between the die 20and the PCB 30. The air bubbles can reduce the effective bond areabetween the die 20 and the PCB 30 and can make the die 20 more likely toseparate from the PCB 30. Furthermore, oxygen in the air bubbles canoxidize the connection between the solder balls 21 and the solder ballpads 22 and/or the bond pads 31 to reduce the integrity of thestructural and/or electrical connections between the die 20 and the PCB30.

Another problem with the process described above with reference to FIGS.2A-2B is that it can be difficult to accurately meter the amount ofunderfill material 40 a applied to the PCB 30. For example, if toolittle underfill material 40 a is provided on the PCB 30, the solderballs 21 may not be adequately covered. Even if the underfill material40 a extends beyond the solder balls 21 to the edge of the die 20 (asindicated in dashed lines in FIG. 2B by position P₁), it can exert atensile force on the die 20 that tends to separate the die 20 from thePCB 30. Conversely, if too much underfill material 40 a is provided onthe PCB 30, the underfill material can extend over the upperwardlyfacing surface 23 of the die 20 (as indicated in dashed lines in FIG. 2Bby position P₂), and can form protrusions 49. The protrusions 49 can besubjected to high stress levels when the die 20 is encapsulated with theencapsulating material 70, and can cause the underfill material 40 a toseparate from the die 20. Still further, the underfill material 40 a canbecome trapped between the solder balls 21 and the bond pads 31 and caninterfere with the electrical connections between the die 20 and the PCB30.

SUMMARY

The present invention is directed toward microelectronic device packagesand methods for forming such packages by bonding microelectronicsubstrates to support members, such as PCBs. A method in accordance withone aspect of the invention includes disposing a fill material in a fillregion defined by a surface of the microelectronic substrate beforeengaging the fill material with the support member. The fill region canalso be defined in part by a bond member (such as a solder ball) orother protrusion projecting away from the surface of the microelectronicsubstrate. The method can further include engaging the fill materialwith the support member after disposing the fill material in the fillregion, and connecting the bond member and the fill material to thesupport member. The microelectronic substrate and the fill material canthen be at least partially enclosed with an encapsulating material.

In one aspect of the invention, the microelectronic substrate is dippedinto a vessel of fill material and is then removed from the vessel witha portion of the fill material attached to the surface of themicroelectronic substrate. Accordingly, the fill material can have athixotropic index with a value of from about four to about six. Inanother aspect of the invention, the surface of the microelectronicsubstrate can be a first surface and the microelectronic substrate caninclude a plurality of second surfaces extending away from the firstsurface, and a third surface facing opposite the first surface. Theextent to which the fill material engages the second surfaces of themicroelectronic substrate can be controlled so that the fill materialengages a portion of the second surfaces extending from the firstsurface to a point about 60% to about 70% of the distance from the firstsurface to the third surface of the microelectronic substrate.

The invention is also directed toward a microelectronic substrateassembly. In one embodiment, the assembly includes a microelectronicsubstrate having a substrate surface and at least one bond memberextending away from the substrate surface and configured to bond to asupport member. A volume of uncured fill material is attached to thesubstrate surface and to the bond member, with the fill material havingan exposed surface to engage the support member. In another aspect ofthe invention, the microelectronic substrate and the bond member areattached to the support member and the fill material has a thixotropicindex of from about four to about six when uncured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic, plan view of a die mounted on a PCB inaccordance with the prior art.

FIGS. 2A-2B illustrate steps in a process for mounting a die to a PCB inaccordance with another prior art method.

FIGS. 3A-3D illustrate a process for mounting a microelectronicsubstrate to a support member in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION

The present disclosure describes packaged microelectronic devices andmethods for manufacturing such devices. Many specific details of certainembodiments of the invention are set forth in the following descriptionand in FIGS. 3A-3D to provide a thorough understanding of theseembodiments. One skilled in the art, however, will understand that thepresent invention may have additional embodiments, and the invention maybe practiced without several of the details described below.

FIG. 3A is a partially schematic, side elevational view of amicroelectronic substrate 120 supported relative to a vessel 150containing a fill material 140 in accordance with an embodiment of theinvention. In one aspect of this embodiment, the microelectronicsubstrate 120 has an upper surface 123, a lower surface 124 opposite theupper surface 123, and four side surfaces 125 extending between theupper surface 123 and the lower surface 124. The microelectronicsubstrate 120 further includes solder ball pads 122 on the lower surface124 that are connected to devices and features (not shown in FIG. 3A)internal to the microelectronic substrate 120. A plurality of bondmembers 121, such as solder balls, are connected to the solder ball pads122. The surfaces of the bond members 121 and the lower surface 124 ofthe microelectronic substrate 120 define a fill region or cavity 126.Alternatively, the microelectronic substrate 120 can have terminalsother than the solder ball pads 122, and/or the bond members 121 caninclude conductive epoxy bumps, metal coated polymer studs or otherconductive elements. In still another embodiment, the microelectronicsubstrate 120 can have other protrusions (that are not necessarilyelectrically conductive) extending away from the lower surface 124. Thefill region 126 of these other embodiments is defined by the lowersurface 124 and the other types of protrusions that project from thelower surface 124.

FIG. 3A illustrates a stage of a method in accordance with an embodimentof the invention in which the substrate 120 is partially submerged inthe fill material 140. In one embodiment, a positioning apparatus 160supports the microelectronic substrate 120 relative to the vessel 150.In one aspect of this embodiment, the positioning apparatus can includea “pick and place” device conventionally used to pick up amicroelectronic substrate for applying flux to solder balls of thesubstrate. The positioning apparatus 160 can include a suction cup 161or another mechanism for releasably engaging the microelectronicsubstrate 120. The apparatus 160 can further include an actuator (notshown) to move the microelectronic substrate 120 laterally as indicatedby arrow M and/or axially as indicated by arrow N. Accordingly, theapparatus 160 can position the microelectronic substrate 120 over thevessel 150, lower the microelectronic substrate 120 a selected distanceinto the fill material 140 within the vessel 150, and remove themicroelectronic substrate 120 from the vessel 150.

In one aspect of this embodiment, the microelectronic substrate 120 ispartially immersed in the fill material 140 by lowering themicroelectronic substrate 120 into the fill material 140 until the lowersurface 124 of the microelectronic substrate 120 is positioned beneath afree surface 141 of the fill material 140. The microelectronic substrate120 is then withdrawn from the vessel 150. Referring now to FIG. 3B, aquantity of the fill material 140 remains attached to themicroelectronic substrate 120 after the microelectronic substrate 120has been withdrawn from the vessel 150 (FIG. 3A). The fill material 140can have an upper surface 142 adjacent to the microelectronic substrate120 and an exposed lower surface 143 facing opposite the upper surface142. The fill material 140 can also extend partially up the sides 125 ofthe microelectronic substrate 120. For example, in one embodiment, thefill material 140 can extend from the lower surface 124 up the sides 125by a distance S₂ that is from about 60% to about 70% of a distance S₁between the lower surface 124 and the upper surface 123. The fillmaterial 140 can also form a thin layer over the lower surfaces of thebond members 121. For example, when the bond members 121 have a diameterD of about 150 microns, the thickness T of the layer of fill material140 adjacent to the bond members 121 can be about 25 microns or less. Inother embodiments, the thickness T of the fill material layer can haveother dimensions, so long as the fill material 140 does not interferewith the electrical connections to the bond members 121, as describedbelow.

Once the microelectronic substrate 120 has been withdrawn from thevessel 150, the positioning apparatus 160 can move the microelectronicsubstrate 120 and the attached fill material 140 into position over asupport member 130, which can include a PCB or another suitablesubstrate. The positioning apparatus 160 then aligns the bond members121 of the microelectronic substrate 120 with corresponding bond pads131 of the support member 130. Referring now to FIG. 3C, the positioningapparatus 160 lowers the microelectronic substrate 120 toward thesupport member 130 until the fill material 140 contacts the supportmember 130. The fill material 140 can also contact the bond pads 131.The positioning apparatus 160 or another apparatus can optionally drivethe microelectronic substrate 120 further downward to press bondingsurfaces of the bond members 121 directly against the bond pads 131 andto squeeze out intervening fill material 140 between the bond members121 and the bond pads 131. As the fill material 140 stabilizes, it canextend partially up the sides 125 of the microelectronic substrate 120by the distance S₂, as described above with reference to FIG. 3B.

When the bond members 121 are solder balls, the bond members 121 can beheated (for example, in a reflow process) to attach the bond members 121to the bond pad 131. The fill material 140 can be cured either as partof the reflow process or in a separate heat cycle to harden the fillmaterial 140 and securely fix the fill material 140 to themicroelectronic substrate 120 and the support member 130. Referring nowto FIG. 3D, an encapsulating material 170 is then disposed over theassembled microelectronic substrate 120 and support member 130 to form apackage 180 that protects the microelectronic substrate 120 and theconnections between the microelectronic substrate 120 and the supportmember 130.

In one embodiment, the fill material 140 can have severalcharacteristics that make it particularly suitable for use with theprocess described above with reference to FIGS. 3A-3D. For example, thefill material 140 can be in a liquid or gel state at room temperature inone embodiment so that the dipping process can be conducted at roomtemperature. In another aspect of this embodiment, the fill material 140can be relatively thick and viscous at room temperature so as to remainattached to the microelectronic substrate 120 when the microelectronicsubstrate 120 is withdrawn from the vessel 150. For example, the fillmaterial 140 can have a thixotropic index of from about four to aboutsix, and in one specific embodiment, the fill material 140 can havethixotropic index of about five. In a further aspect of this embodiment,the fill material 140 can include a conventional underfill epoxymaterial thickened to achieve the desired thixotropic index. Forexample, the fill material 140 can include FF 2000 epoxy (available fromDexter Labs of City of Industry, Calif.), which has an initialthixotropic index of from about one to about two. The epoxy can bethickened with thickening agents (such as barium sulfate) to increasethe thixotropic index to a value of from about four to about six.Alternatively, the fill material 140 can have other suitablecompositions and formulations.

In still another aspect of an embodiment of the process described abovewith reference to FIGS. 3A-3D, the fill material 140 can include a smallamount of a surfactant, for example, about 1% or less by volume.Accordingly, the fill material 140 can have a reduced tendency (whencompared to conventional underfill materials) for forming voids orpockets (a) at the interface between the microelectronic substrate 120and the fill material 140 when the microelectronic substrate 120 ispartially immersed in the fill material 140, and (b) at the interfacebetween the fill material 140 and the support member 130 when themicroelectronic substrate 120 is mounted to the support member 130. Anadvantage of this arrangement is that the fill material 140 is morelikely to form a secure and hermetically sealed bond between themicroelectronic substrate 120 and the support member 130.

Another advantage of an embodiment of the process described above withreference to FIGS. 3A-3D is that the amount of fill material 140attached to each microelectronic substrate 120 can be controlled. Forexample, the height S₂ to which the fill material 140 extends up thesides 125 of the microelectronic substrate 120 can be controlled bycontrolling the thixotropic index and wettability of the fill material140, and the depth to which the microelectronic substrate 120 isimmersed in the fill material 140. Furthermore, the thickness T of thefill material 140 adjacent to the solder balls 121 can be controlled bycontrolling the thixotropic index of the fill material 140. Stillfurther, the total amount of fill material 140 that adheres to themicroelectronic substrate 120 varies with the size of themicroelectronic substrate 120, and in particular, the surface area ofthe lower surface 124. For example, as the size of the lower surface 124increases, the amount of fill material 140 adhering to the lower surface124 increases correspondingly. Accordingly, the amount of fill material140 adhering to each microelectronic substrate 120 self-adjusts to thesize of the microelectronic substrate 120. This is unlike someconventional underfill methods described above with reference to FIGS.1-2B which require changing the amount of underfill material applied tothe PCB whenever the size of the microelectronic substrate is changed.

Yet another advantage of an embodiment of the process described abovewith reference to FIGS. 3A-3D is that the relatively high thixotropicindex of the fill material 140 can increase the strength of the initialbond between the uncured liquid or gel fill material 140, themicroelectronic substrate 120, and the support member 130 (i.e., the“green strength” of the bond). For example, the more viscous fillmaterial 140 can more securely support the microelectronic substrate 120in position on the support member 130 during the interim period betweenattaching the microelectronic substrate 120 to the support member 130and curing the fill material 140. This feature can be advantageousbecause the microelectronic substrate 120 is expected to be less likelyto move relative to the support member 130 during operations that takeplace before the fill material 140 is cured. Such operations can includemoving the microelectronic substrate 120 and support member 130 from oneprocessing station to the next and/or reflowing the bond members 121.

In other embodiments, the processes and materials described above withreference to FIGS. 3A-3D can have other configurations and arrangements.For example, in one alternate embodiment, the temperature of thereservoir 150 can be controlled to control the viscosity of the fillmaterial 140. In another alternate embodiment, the fill material 140 canbe disposed on the microelectronic substrate 120 by processes other thandipping. For example, the fill material 140 can be sprayed onto themicroelectronic substrate 120 in one or more coats, or the fill material140 can be deposited in the fill region using stencil printing orpen-type dispensers known in the surface mounting technology arts.

In still further embodiments, the fill material 140 can have suitableconfigurations other than the configurations described above. The fillmaterial 140, for example, can be any type of material that can beapplied to the lower surface of the microelectronic substrate 120 beforeattaching the substrate 120 to a support member 130 for filling the gapbetween the substrate 120 and the support member 130. Moreover, the bondmembers 121 need not include solder balls, and/or the microelectronicsubstrate 120 can have protrusions other than bond members that define afill region or cavity adjacent to the lower surface 124. In yet anotherembodiment, the microelectronic substrate 120 can have no protrusions,so long as the fill material 140 is applied to the lower surface 124 ora portion of the lower surface 124 prior to attaching themicroelectronic substrate 120 to the support member 130. In one aspectof this embodiment, the bond members 121 can first be attached to thesupport member 130 and then connected to terminals (such as bond pads)of the microelectronic substrate 120 that are flush with the lowersurface 124 of the microelectronic substrate 120. In still anotherembodiment, the pre-disposed fill material 140 can be supplemented withadditional fill material disposed on the support member 130 in a mannergenerally similar to that described above with reference to FIG. 1 orFIGS. 2A-2B.

From the foregoing, it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without from deviatingfrom the spirit and scope of the invention. Accordingly, the inventionis not limited except as by the appended claims.

What is claimed is:
 1. A microelectronic substrate assembly formed by amethod, comprising: disposing a quantity of fill material in a cavitydefined by a surface of the microelectronic substrate and a bond memberprojecting away from the surface of the microelectronic substrate beforeengaging the fill material with a support member, wherein disposing thefill material in the cavity includes dipping the microelectronicsubstrate in a vessel of fill material and removing the microelectronicsubstrate from the vessel with a portion of the fill material attachedto the surface of the microelectronic substrate; engaging the fillmaterial with the support member after disposing the fill material inthe cavity; and connecting the bond member and the fill material to thesupport member.
 2. The microelectronic substrate assembly of claim 1wherein the bond member includes a solder ball and wherein connectingthe bond member includes connecting the solder ball.
 3. Themicroelectronic substrate assembly of claim 1 wherein engaging the fillmaterial includes engaging the fill material when the fill material isin an at least partially uncured state, and wherein the method furthercomprises curing the fill material after connecting the bond member andthe fill material to the support member.
 4. The microelectronicsubstrate assembly of claim 1 wherein the surface of the microelectronicsubstrate is a first surface and wherein the microelectronic substrateincludes a plurality of second surfaces extending away from the firstsurface, and wherein the method further comprises disposing at least aportion of the fill material adjacent to at least one of the secondsurfaces of the microelectronic substrate.
 5. A microelectronicsubstrate assembly including a microelectronic substrate having a firstsurface, a plurality of second surfaces extending away from the firstsurface, the microelectronic substrate assembly being formed by amethod, comprising: dipping the microelectronic substrate into areservoir of flowable fill material at least until the first surface ofthe microelectronic substrate is positioned beneath a free surface ofthe fill material in the reservoir and the fill material contacts thesecond surfaces of the microelectronic substrate; disposing a quantityof fill material in a cavity defined by a surface of the microelectronicsubstrate and a bond member projecting away from the surface of themicroelectronic substrate before engaging the fill material with asupport member; engaging the fill material with the support member afterdisposing the fill material in the cavity; and connecting the bondmember and the fill material to the support member.
 6. Themicroelectronic substrate assembly of claim 5 wherein the bond memberincludes a solder ball and wherein connecting the bond member includesconnecting the solder ball.
 7. The microelectronic substrate assembly ofclaim 5 wherein engaging the fill material includes engaging the fillmaterial when the fill material is in an at least partially uncuredstate, and wherein the method further comprises curing the fill materialafter connecting the bond member and the fill material to the supportmember.
 8. A microelectronic substrate assembly formed by a method,comprising: disposing a quantity of fill material in a cavity defined bya surface of the microelectronic substrate and a bond member projectingaway form the surface of the microelectronic substrate before engagingthe fill material with a support member, the fill material having athixotropic index of from about four to about six; engaging the fillmaterial with the support member after disposing the fill material inthe cavity; and connecting the bond member and the fill material to thesupport member.
 9. The microelectronic substrate assembly of claim 8wherein the bond member includes a solder ball and wherein connectingthe bond member includes connecting the solder ball.
 10. Themicroelectronic substrate assembly of claim 8 wherein engaging the fillmaterial includes engaging the fill material when the fill material isin an at least partially uncured state, and wherein the method furthercomprises curing the fill material after connecting the bond member andthe fill material to the support member.
 11. The microelectronicsubstrate assembly of claim 8 wherein the surface of the microelectronicsubstrate is a first surface and wherein the microelectronic substrateincludes a plurality of second surfaces extending away from the firstsurface, and wherein the method further comprises disposing at least aportion of the fill material adjacent to at least one of the secondsurfaces of the microelectronic substrate.
 12. A microelectronicsubstrate assembly formed by a method, comprising: disposing a quantityof fill material in a cavity defined by a surface of the microelectronicsubstrate and a bond member projecting away from the surface of themicroelectronic substrate before engaging the fill material with asupport member; engaging the fill material with the support member afterdisposing the fill material in the cavity; connecting the bond memberand the fill material to the support member, wherein the fill materialis initially in a flowable state; and curing the fill material tosolidify the fill material.
 13. The microelectronic substrate assemblyof claim 12 wherein the bond member includes a solder ball and whereinconnecting the bond member includes connecting the solder ball.
 14. Themicroelectronic substrate assembly of claim 12 wherein engaging the fillmaterial includes engaging the fill material when the fill material isin an at least partially uncured state, and wherein the method furthercomprises curing the fill material after connecting the bond member andthe fill material to the support member.
 15. A microelectronic substrateassembly formed by a method, comprising: disposing a quantity of fillmaterial in a cavity defined by a surface of the microelectronicsubstrate and a bond member projecting away from the surface of themicroelectronic substrate before engaging the fill material with asupport member, wherein the bond member includes a solder ball having adiameter of about 150 microns and a bonding surface facing away from themicroelectronic substrate, and wherein disposing the fill materialincludes disposing the fill material to a thickness of about 25 micronsor less beyond the bonding surface of solder balls.
 16. Amicroelectronic substrate assembly for mounting to a support member,comprising: a microelectronic substrate having a first surface and aplurality of second surfaces extending away from the first surface, athird surface facing in a direction opposite the first surface, and atleast one bond member extending away from the substrate surface todefine a fill region on the substrate surface, the bond member beingconfigured to be bonded to the support member; and a volume of uncuredfill material disposed in the fill region and having a first surfaceattached to at least the substrate surface, the fill material having asecond surface exposed before attaching the microelectronic substrate tothe support member wherein the fill material engages a portion of thesecond surfaces extending from the first surface to a point from about60% to about 70% of the distance from the first surface to the thirdsurface of the microelectronic substrate.
 17. The microelectronicsubstrate of claim 16 wherein the at least one bond member includes asolder ball.
 18. A microelectronic substrate assembly for mounting to asupport member, comprising: a microelectronic substrate having asubstrate surface and at least one bond member extending away from thesubstrate surface to define a fill region on the substrate surface, thebond member being configured to be bonded to the support member, whereinthe bond member includes a solder ball having a diameter of about 150microns and a bonding surface facing away from the microelectronicsubstrate; a volume of uncured fill material disposed in the fill regionand having a first surface attached to at least the substrate surface,the fill material having a second surface exposed before attaching themicroelectronic substrate to the support member, wherein the fillmaterial has a thickness of about 25 microns or less beyond the bondingsurface of the solder ball.
 19. The microelectronic substrate assemblyof claim 18 wherein the substrate surface is a first substrate surfaceand wherein the microelectronic substrate includes at least one secondsubstrate surface extending away from the first substrate surface, and athird substrate surface facing opposite the first substrate surface, andwherein the fill material engages a portion of the at least one secondsurface extending from the first substrate surface to a point about 60%to about 70% of the distance from the first substrate surface to thethird substrate surface.
 20. A microelectronic substrate assembly formounting to a support member, comprising: a microelectronic substratehaving a substrate surface and at least one bond member extending awayfrom the substrate surface to define a fill region on the substratesurface, the bond member being configured to be bonded to the supportmember; and a volume of uncured fill material disposed in the fillregion and having a first surface attached to at least the substratesurface, the fill material having a second surface exposed beforeattaching the microelectronic substrate to the support member, whereinthe fill material has a thixotropic index of from about four to aboutsix.
 21. The microelectronic substrate assembly of claim 20 wherein theat least one bond member includes a solder ball.
 22. The microelectronicsubstrate assembly of claim 20 wherein the substrate surface is a firstsubstrate surface and wherein the microelectronic substrate includes atleast one second substrate surface extending away from the firstsubstrate surface and a third substrate surface facing opposite thefirst substrate surface, and wherein the fill material engages a portionof the at least one second substrate surface extending from the firstsubstrate surface to a point about 60% to about 70% of the distance fromthe first substrate surface to the third substrate surface.
 23. Amicroelectronic substrate assembly for mounting to a support member,comprising: a microelectronic substrate having a substrate surface andat least one bond member extending away from the substrate surface todefine a fill region on the substrate surface, the bond member beingconfigured to be bonded to the support member; and a volume of uncuredfill material disposed in the fill region and having a first surfaceattached to at least the substrate surface, the fill material having asecond surface exposed before attaching the microelectronic substrate tothe support member, wherein the fill material has a thixotropic index ofabout five.
 24. The microelectronic substrate assembly of claim 23wherein the at least one bond member includes a solder ball.
 25. Themicroelectronic substrate assembly of claim 23 wherein the substratesurface is a first substrate surface and wherein the microelectronicsubstrate includes at least one second substrate surface extending awayfrom the first substrate surface and a third substrate surface facingopposite the first substrate surface, and wherein the fill materialengages a portion of the at least one second substrate surface extendingfrom the first substrate surface to a point about 60% to about 70% ofthe distance from the first substrate surface to the third substratesurface.
 26. A microelectronic substrate assembly for mounting to asupport member, comprising: a microelectronic substrate having asubstrate surface and at least one bond member extending away from thesubstrate surface to define a fill region on the substrate surface, thebond member being configured to be bonded to the support member; and avolume of uncured fill material disposed in the fill region and having afirst surface attached to at least the substrate surface, the fillmaterial having a second surface exposed before attaching themicroelectronic substrate to the support member, wherein the fillmaterial includes an uncured epoxy.
 27. The microelectronic substrateassembly of claim 26 wherein the at least one bond member includes asolder ball.
 28. A microelectronic device assembly, comprising: asupport member having a support member surface and a plurality of bondsites proximate to the support member surface; a microelectronicsubstrate having a substrate surface and a plurality of bond membersprojecting away from the substrate surface and attached to the bondsites with the substrate surface facing toward the support membersurface; and a fill material disposed between the support member surfaceand the substrate surface, the fill material having an uncured statethixotropic index of from about four to about six.
 29. The assembly ofclaim 28 wherein the substrate surface is a first surface and themicroelectronic substrate has a plurality of second surfaces extendingaway from the first surface and a third surface facing in a directionopposite the first surface, and wherein the fill material engages aportion of the second surfaces extending from the first surface to apoint about 60% to about 70% of the distance from the first surface tothe third surface of the microelectronic substrate.
 30. The assembly ofclaim 28 wherein the fill material has a thixotropic index of aboutfive.
 31. The assembly of claim 28, further comprising an encapsulatingmaterial at least partially surrounding the microelectronic substrateand the fill material.